The present invention relates to a novel polymer, and a light emitting element containing the polymer, with the excellent high luminance light emission, high light emission efficiency and durability.
Recently, study and development have been executed actively on various kinds of display elements. In particular, an organic electroluminescence (EL) element capable of obtaining high luminance light emission with a low voltage has been attracting attention as a prospective display element. For example, an EL element with an organic thin film formed by depositing an organic compound is known (Applied Physics Letters, 51, p. 913-, (1987)) The organic EL element disclosed in the literature has a laminated structure of an electric transporting material and a hole transporting material. It has a dramatically improved light emission characteristic compared with the conventional single layer type elements.
According to the laminated type element, the element is formed by depositing a low molecular organic material as the element material. As a technique for forming the thin film used in the organic EL element, various methods such as a vacuum deposition method as in the above-mentioned literature, a sputtering method, a CVD, a PVD, a coating method using a solvent, or the like can be used. Details thereof are described in the content of some documents. Examples thereof include ORGANIC ELECTROLUMINESCENT MATERIALS AND DEVICES (OPA, Amsterdam, 1997), Organic EL element and Industrialization Front Line Thereof (NTS, 1998), or the like. The present inventor has discussed a method of coating a solution of an organic compound, in particular, an organic polymer material as the thin film forming technique. In the case of the organic polymer material, a thin film can be formed with little defect by the material alone, and the formed thin film can provide characteristics of the excellent physical and chemical fastness.
However, in the case a plurality of materials having various functions such as the electron transporting property, the electron injecting property, the hole transporting property, the hole injecting property and the light emitting property is used for a light emitting element, phase separation, or the like can frequently be generated at the time of mixing the organic polymer materials, and thus it was learned that it is problematic in terms of the performance. Moreover, even in the case of using a low molecular compound mixed with a polymer material, it was learned that it is problematic in terms of the durability.
As an attempt for solving the above-mentioned problem, a method of copolymerizing monomers having various functions is conceivable. However, according to the study and discussion of the present inventor, it was learned that a sufficient performance cannot be obtained by a simple copolymer.
According to a general light emitting element, the light emitting efficiency can be improved by using a hole transporting compound and an electron transporting compound in laminated layers or in the same layer. The present inventor has discussed an element using a plurality of materials in a coating type organic EL element. As to a light emitting element material to be used for a coating type light emitting element, an electron rich hetero aromatic compound such as a pyrrole, a thiophene and a furan is effective as the hole transporting compound. Moreover, an electron deficient hetero aromatic compound containing a plurality of hetero electrons is effective as the electron transporting compound. However, as mentioned above, in the case a plurality of functional materials are used for a light emitting element, it was learned that only a low light emitting performance can be obtained with organic polymer materials. Moreover, in the case a low molecular compound is used as a mixture with a polymer material, it was learned that a problems arises in terms of the durability.
Japanese Patent Application Laid-Open Specification No. 2000-286056 discloses an EL element material containing a carbazole derivative. Japanese Patent Application Laid-Open Specification No. 9-255725/1997 discloses a method for producing an oxadiazolylated polymer usable as an electron transport material of an organic electroluminescent element by selecting a polymer having oxadiazole groups at the side chains.
A first object of the invention is to provide a novel polymer. A second object is to provide a light emitting element using the same, capable of emitting a light with a high luminance and a good light emitting efficiency, and having the excellent durability.
The invention was achieved by the below-mentioned polymer and light emitting element:
1. A polymer represented by the below-mentioned formula (1):
(Am)p-(Bn)q-(Ck)rxe2x80x83xe2x80x83(1)
(wherein A represents a monomer unit including a pyrrole, a thiophene, a furan and aromatic and hetero aromatic condensed ring derivatives, B represents a monomer unit including a hetero ring derivative containing two or more hetero atoms in a ring system, C represents a monomer unit having a structure other than the above-mentioned, m and n represent an integer of 1 or more, k represents an integer of 0 or more, p and q each denote a mole percentage (%) of 1-99(%), r represents 0-98(%) with the premise that p+q+r=100(%), and a ballast group having 4 or more carbon atoms is substituted at least in one of the A, B and C monomer units);
2. The polymer according to the above-mentioned item 1, wherein at least one of A in the formula (1) is a monomer unit including a carbazole derivative and at least one of B is a monomer unit including a 1,3,4-oxadiazole derivative;
3. The polymer according to the above-mentioned items 1 to 2, wherein the monomer units in the formula (1) are a vinyl monomer unit;
4. A light emitting element provided by coating at least one or more kinds of polymers between an anode and a cathode, wherein at least one of the polymers contains the polymer according to the above-mentioned items 1 to 3; and
5. The light emitting element according to the above-mentioned items 1 to 4, wherein at least one kind of a light emitting material capable of emitting a light from a triplet exciter is used as a light emitting material.